1. Field of the Invention
The present invention concerns a process for the inspection of the surface of a mill roll, and more generally of a cylindrical body. It likewise relates to a device for implementing this process.
2. Description of the Related Art
There are numerous applications in the industry in which the condition of the surface of a manufacturing tool at least partially determines the quality of the manufactured product. One extremely important particular instance is that of the manufacture of steel strips, the surface finish of which depends to a large extend on the condition of the surface of the working rolls of the rolling mill.
In the course of rolling, in fact, the surface of the working rolls progressively deteriorates due to oxidation, incrustation of oxide particles, cracking caused by thermal shocks or indeed tearing of metal films under the effect of superficial stresses. It is therefore important to inspect the surface of mill rolls regularly, especially the surface of the lower working rolls of the first finishing stands, which wear particularly rapidly.
Initially, inspection of the surface of the rolls consisted in a simple visual examination by an operator when it came to replacing the working rolls. In certain cases, intermediate inspections were required, owing to the presence of defects in the rolled strips for example. It was then necessary to stop the rolling mill and sometimes even to remove the rolls. These intermediate unscheduled stops take a lot of time and entail a loss of productivity. Apart from this disadvantage, the subjective nature of such visual inspections can affect the quality of the examination, which consequently no longer meets current requirements of reliability, reproducibility and rapidity.
Processes and devices for inspecting the surface of mill rolls are of course already known in the prior art, in particular by means of cameras equipped with illumination means and arranged close to the rolls to be inspected. Generally speaking, however, the known systems have the disadvantage of inspecting the surface in a fixed direction.
For the inspection of a surface to be satisfactorily carried out, it should ideally be performed in a specular manner, i.e. that the direction of inspection should be perpendicular to the surface at the point of observation. In the case of surfaces such as those of mill rolls, inspection in a fixed direction rapidly loses any possible specular feature that it might initially have had as the diameter of the rolls decreases due to the straightening operations on the surface of the roll, which are intended to eliminate the defects that have appeared at their surface.